Red blood cells have a 2-3 month "lifespan" (I forget exactly), so there really aren't things like "off" days in the RBC count.
Overhydration is one short-term thing that could lower the RBC count very temporarily.
Your symptoms sound anemic to me. You may want to check your mentioned symptoms (plus any others you have) against this list:
http://en.wikipedia.org/wiki/Lead_po...ms_and_effects